1. Field of the Invention
The present invention relates to a composite thin-film magnetic head comprising a reproducing head and a recording head and to a method of manufacturing such a thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as surface recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading.
It is required to increase the track density on a magnetic recording medium in order to increase recording density among the performance characteristics of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein a track width, that is, the width of top and bottom poles sandwiching the recording gap layer on a side of the air bearing surface, is reduced down to microns or the submicron order. Semiconductor process techniques are utilized to implement such a structure.
Reference is now made to FIG. 23A to FIG. 26A and FIG. 23B to FIG. 26B to describe an example of a method of manufacturing a composite thin-film magnetic head as an example of a related-art method of manufacturing a thin-film magnetic head. FIG. 23A to FIG. 26A are cross sections each orthogonal to an air bearing surface of the thin-film magnetic head. FIG. 23B to FIG. 26B are cross sections of a pole portion of the head each parallel to the air bearing surface.
In the manufacturing method, as shown in FIG. 23A and FIG. 23B, an insulating layer 102 made of alumina (Al2O3), for example, having a thickness of about 5 to 10 μm is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. On the insulating layer 102 a bottom shield layer 103 made of a magnetic material is formed for making a reproducing head.
Next, on the bottom shield layer 103, alumina, for example, is deposited to a thickness of 100 to 200 nm through sputtering to form a bottom shield gap film 104 as an insulating layer. On the bottom shield gap film 104 an MR element 105 for reproduction having a thickness of tens of nanometers is formed. Next, a pair of electrode layers 106 are formed on the bottom shield gap film 104. The electrode layers 106 are electrically connected to the MR element 105.
Next, a top shield gap film 107 is formed as an insulating layer on the bottom shield gap film 104 and the MR element 105. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, on the top shield gap film 107, a top-shield-layer-cum-bottom-pole-layer (called a bottom pole layer in the following description) 108 having a thickness of about 3 μm is formed. The bottom pole layer 108 is made of a magnetic material and used for both a reproducing head and a recording head.
Next, as shown in FIG. 24A and FIG. 24B, on the bottom pole layer 108, a recording gap layer 109 made of an insulating film such as an alumina film whose thickness is 0.2 μm is formed. Next, a portion of the recording gap layer 109 is etched to form a contact hole 109a to make a magnetic path. On the recording gap layer 109 in the pole portion, a top pole tip 110 made of a magnetic material and having a thickness of 0.5 to 1.0 μm is formed for the recording head. At the same time, a magnetic layer 119 made of a magnetic material is formed for making the magnetic path in the contact hole 109a for making the magnetic path.
Next, as shown in FIG. 25A and FIG. 25B, the recording gap layer 109 and the bottom pole layer 108 are etched through ion milling, using the top pole tip 110 as a mask. As shown in FIG. 25B, the structure is called a trim structure wherein the sidewalls of the top pole (the top pole tip 110), the recording gap layer 109, and a part of the bottom pole layer 108 are formed vertically in a self-aligned manner.
Next, an insulating layer 111 made of an alumina film, for example, and having a thickness of about 3 μm is formed on the entire surface. The insulating layer 111 is then polished to the surfaces of the top pole tip 110 and the magnetic layer 119 and flattened.
Next, on the flattened insulating layer 111, a first layer 112 of a thin-film coil is made of copper (Cu), for example, for the induction-type recording head. Next, a photoresist layer 113 is formed into a specific shape on the insulating layer 111 and the first layer 112. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer 113. On the photoresist layer 113, a second layer 114 of the thin-film coil is then formed. Next, a photoresist layer 115 is formed into a specific shape on the photoresist layer 113 and the second layer 114. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer 115.
Next, as shown in FIG. 26A and FIG. 26B, a top pole layer 116 is formed for the recording head on the top pole tip 110, the photoresist layers 113 and 115, and the magnetic layer 119. The top pole layer 116 is made of a magnetic material such as Permalloy. Next, an overcoat layer 117 of alumina, for example, is formed to cover the top pole layer 116. Finally, lapping of the slider is performed to form the air bearing surface 118 of the thin-film magnetic head including the recording head and the reproducing head. The thin-film magnetic head is thus completed.
FIG. 27 is a top view of the thin-film magnetic head shown in FIG. 26A and FIG. 26B. The overcoat layer 117 and the other insulating layers and insulating films are omitted in FIG. 27.
In FIG. 26A, ‘TH’ indicates the throat height and ‘MR-H’ indicates the MR height. The throat height is the length (height) of pole portions, that is, portions of magnetic pole layers facing each other with a recording gap layer in between, the length between the air-bearing-surface-side end and the other end. The MR height is the length (height) between the air-bearing-surface-side end of the MR element and the other end. In FIG. 26B, ‘P2W’ indicates the pole width, that is, the track width of the recording head (hereinafter called the recording track width). In addition to the factors such as the throat height and the MR height, the apex angle as indicated with θ in FIG. 26A is one of the factors that determine the performance of a thin-film magnetic head. The apex is a hill-like raised portion of the coil covered with the photoresist layers 113 and 115. The apex angle is the angle formed between the top surface of the insulating layer 111 and the straight line drawn through the edges of the pole-side lateral walls of the apex.
In order to improve the performance of the thin-film magnetic head, it is important to precisely form throat height TH, MR height MR-H, apex angle θ, and track width P2W as shown in FIG. 26A and FIG. 26B.
To achieve high surface recording density, that is, to fabricate a recording head with a narrow track structure, it has been particularly required that track width P2W fall within the submicron order of 1.0 μm or less. It is therefore required to process the top pole of the submicron order through semiconductor process techniques.
A problem is that it is difficult to form the top pole layer of small dimensions on the apex.
As disclosed in Published Unexamined Japanese Patent Application Hei 7-262519 (1995), for example, frame plating may be used as a method for fabricating the top pole layer. In this case, a thin electrode film made of Permalloy, for example, is formed by sputtering, for example, to fully cover the apex. Next, a photoresist is applied to the top of the electrode film and patterned through a photolithography process to form a frame to be used for plating. The top pole layer is then formed by plating through the use of the electrode film previously formed as a seed layer.
However, there is a difference in height between the apex and the other part, such as 7 to 10 μm or more. The photoresist whose thickness is 3 to 4 μm is applied to cover the apex. If the photoresist thickness is required to be at least 3 μm over the apex, a photoresist film having a thickness of 8 to 10 μm or more, for example, is formed below the apex since the fluid photoresist goes downward.
To implement a recording track width of the submicron order as described above, it is required to form a frame pattern having a width of the submicron order through the use of a photoresist film. Therefore, it is required to form a fine pattern of the submicron order on top of the apex through the use of a photoresist film having a thickness of 8 to 10 μm or more. However, it is extremely difficult to form a photoresist pattern having such a thickness into a reduced pattern width, due to restrictions in a manufacturing process.
Furthermore, rays of light used for exposure of photolithography are reflected off the base electrode film as the seed layer. The photoresist is exposed to the reflected rays as well and the photoresist pattern may go out of shape. It is therefore impossible to obtain a sharp and precise photoresist pattern.
In the region on the slope of the apex, in particular, the rays reflected off the bottom electrode film include not only vertical reflected rays but also rays in slanting directions and rays in lateral directions from the slope of the apex. As a result, the photoresist is exposed to those reflected rays of light and the photoresist pattern more greatly goes out of shape.
With regard to the track width, it is required that the amount of lapping the slider will not affect the track width.
Therefore, when the top pole layer is formed on the apex, some means is required for reducing the effect on the track width of the rays reflected off the bottom electrode film during exposure of the photolithography process.
For example, the top pole layer of a prior-art thin film magnetic head has the shape including a portion having a width equal to the track width. This portion is located between the air bearing surface and a point at a distance of only 3 to 5 μm, for example, from the zero throat height position (the position of an end of the pole portion opposite to the air bearing surface) toward the apex. A portion of the top pole layer next to the portion having a width equal to the track width has a width extending toward the coil at an obtuse angle of 30 or 45 degrees.
However, if the top pole layer has the shape as described above, a magnetic flux is saturated near the zero throat height position and it is impossible to efficiently utilize the magnetomotive force generated by the coil for writing. As a result, the value indicating an overwrite property is reduced down to about 10 to 20 dB, for example. The overwrite property is a parameter indicating one of characteristics when data is written over existing data on a recording medium. It is therefore difficult to obtain a sufficient overwrite property.
In addition, if the top pole layer has the shape as described above, a portion of the top pole layer whose width starts to extend is located on the slope of the apex. However, if the top pole layer has such a shape and is located in such a manner, the photoresist pattern is particularly susceptible to the rays reflected off the bottom electrode film. It is therefore difficult to precisely control the track width.
As thus described, the problem of the prior art is that it is difficult to precisely control the track width if the track width of the submicron order is required and that a magnetic flux is likely to saturate near the zero throat height position.
In order to implement a thin-film magnetic head that achieves surface recording density of 10 to 40 gigabits per square inches, for example, or a thin-film magnetic head that performs recording in a good condition at a frequency as high as 300 to 600 MHz, for example, it is particularly important to form a reduced track width with uniformity and to utilize the magnetomotive force generated by the coil with efficiency for writing. It is therefore strongly required to solve the above-mentioned problems.
To overcome the problems thus described, a method has been taken, as shown in the foregoing related-art manufacturing steps illustrated in FIG. 24A to FIG. 26A and FIG. 24B to FIG. 26B. In this method, a track width of 1.0 μm or less is formed through the use of the top pole tip 110 effective for making a narrow track of the recording head. The top pole layer 116 to be a yoke portion connected to the top pole tip 110 is then fabricated (as disclosed in Published Unexamined Japanese Patent Application Sho 62-245509 [1987] and Published Unexamined Japanese Patent Application Sho 60-10409 [1985]). That is, the ordinary top pole layer is divided into the top pole tip 110 and the top pole layer 116 to be the yoke portion in this method. As a result, it is possible that the top pole tip 110 that defines the track width is formed into small dimensions to some degree on the flat top surface of the recording gap layer 109.
However, the following problems are still found in the thin-film magnetic head having a structure as shown in FIG. 26A and FIG. 26B.
In the thin-film magnetic head shown in FIG. 26A and FIG. 26B, the recording track width is defined by the top pole tip 110. Therefore, it is not necessary that the top pole layer 116 is processed into dimensions as small as those of the top pole tip 110. However, if the recording track width is extremely reduced, that is, down to 0.5 μm or less, in particular, processing accuracy for achieving the submicron-order width is required for the top pole layer 116, too. However, the top pole layer 116 is formed on top of the apex in the head shown in FIG. 26A and FIG. 26B. Therefore, it is difficult to reduce the top pole layer 116 in size, due to the reason described above. In addition, the top pole layer 116 is required to be greater than the top pole tip 110 in width since the top pole layer 116 is required to be magnetically connected to the top pole tip 110 smaller in width. Because of these reasons, the top pole layer 116 is greater than the top pole tip 110 in width in this thin-film magnetic head. In addition, the end face of the top pole layer 116 is exposed from the air bearing surface. As a result, writing may be performed by the thin-film magnetic head on a side of the top pole layer 116, too, and so-called ‘side write’ may result, that is, data is written in a region of a recording medium where data is not supposed to be written. Such a problem more frequently results when the coil is two-layer or three-layer to improve the performance of the recording head and the apex is thereby increased in height, compared to the case where the coil is one-layer.
In the thin-film magnetic head shown in FIG. 26A and FIG. 26B, the recording track width and the throat height are defined by the top pole tip 110. Therefore, if the recording track width is extremely reduced, that is, down to 0.5 μm or less, in particular, the size of the top pole tip 110 is thus extremely reduced. As a result, pattern edges may be rounded and it is difficult to form the top pole tip 110 with accuracy. Therefore, the thin-film magnetic head having the structure as shown in FIG. 26A and FIG. 26B has a problem that it is difficult to precisely define the recording track width and the throat height if the recording track width is extremely reduced.
In the thin-film magnetic head shown in FIG. 26A and FIG. 26B, the cross-sectional area of the magnetic path abruptly decreases in a portion where the top pole layer 116 is in contact with the top pole tip 110. Consequently, the magnetic flux is saturated in this portion, and it is impossible to efficiently utilize the magnetomotive force generated by the layers 112 and 114 of the thin-film coil for recording.
Furthermore, it is difficult to reduce the magnetic path (yoke) length of a prior-art magnetic head. That is, if the coil pitch is reduced, a head with a reduced yoke length is achieved and a recording head having an excellent high frequency characteristic is achieved, in particular. However, if the coil pitch is reduced to the limit, the distance between the zero throat height position (the position of the air-bearing-surface-side end of the insulating layer that defines the throat height) and the outermost end of the coil is a major factor that prevents a reduction in yoke length. Since the yoke length of a two-layer coil can be shorter than that of a single-layer coil, a two-layer coil is adopted to many of recording heads for high frequency application. However, in the prior-art magnetic head, a photoresist film having a thickness of about 2 μm is formed to provide an insulating film between coil layers after a first layer is formed. Consequently, a small and rounded apex is formed at the outermost end of the first layer of the coil. A second layer of the coil is then formed on the apex. The second layer is required to be formed on a flat portion since it is impossible to etch the seed layer of the coil in the sloped portion of the apex, and the coil is thereby shorted.
Therefore, if the total coil thickness is 2 to 3 μm, the thickness of the insulating film between the layers of the coil is 2 μm, and the apex angle is 45 to 55 degrees, for example, the yoke length is required to be 6 to 8 μm which is twice as long as the distance between the outermost end of the coil and the neighborhood of the zero throat height position, that is, 3 to 4 μm (the distance between the innermost end of the coil and the portion where the top and bottom pole layers are in contact with each other is required to be 3 to 4 μm, too), in addition to the length of the portion corresponding to the coil. This length of the portion other than the portion corresponding to the coil is one of the factors that prevent a reduction in yoke length.
Assuming that a two-layer eleven-turn coil in which the line width is 1.2 μm and the space is 0.8 μm is fabricated, for example, the portion of the yoke length corresponding to the first layer 112 of the coil is 11.2 μm, if the first layer is made up of six turns and the second layer is made up of 5 turns, as shown in FIG. 26A and FIG. 26B. In addition to this length, the total of 6 to 8 μm, that is, the distance between each of the outermost and innermost ends of the first layer 112 of the coil and each of ends of the photoresist layer 113 for insulating the first layer 112, is required for the yoke length. Therefore, the yoke length is 17.5 to 19.5 μm. In the present patent application, the yoke length is the length of a portion of the pole layer except the pole portion and the contact portions, as indicated with L0 in FIG. 26A. As thus described, it is difficult in the prior art to further reduce the yoke length, which prevents improvements in high frequency characteristic.